1. Field of the Invention
The present invention relates to a non-porous hydrogen diffusion membrane, and to the utilization thereof for the separation of hydrogen from gas mixtures.
2. Discussion of the Prior Art
The separation of hydrogen from gas mixtures is known based on diffusion through a diffusion membrane or diffusion wall which is constituted of palladium. Presently known are also diffusion walls which are constituted of other hydrogen-permeable materials, which are coated with palladium or palladium alloys on only the gas inlet side; in effect, on the side which is exposed to the gas mixture. Thus, for example, pursuant to U.S. Pat. No. 3,407,571 there are employed diffusion walls which are formed, for instance, of steel, and which are coated on the primary side with a thin palladium layer or palladium alloy such as, for example, a palladium-silver alloy containing up to about 60% of silver. In order to accelerate the diffusion, such walls should be especially employed at an elevated temperature, which can reach up to about 820.degree. C., wherein temperatures are preferred in the range of about 150.degree. to 260.degree. C. Furthermore, there should be particularly maintained a pressure differential between the primary and secondary side, which lies at least at about 1 bar, and preferably can extend up to about 100 bar.
In accordance with the disclosure of U.S. Pat. No. 1,174,631, the separation of hydrogen from gas mixtures can be carried out continuously and especially economically by means of diffusion through a platinum or palladium wall having a porous ceramic substrate, wherein the hydrogen which has been released after diffusion is then conveyed off.
In the practical implementation of such processes for the separation of hydrogen by means of diffusion through non-porous partition walls, which are permeable only to hydrogen, difficulties are encountered particularly during operation at elevated temperatures, and with the separation in the form of light hydrogen or its isotopes, such as would, for example, be encountered in the primary cooling gas of a nuclear reactor; inasmuch as over lengthier time periods some minor contamination of the primary or secondary chambers themselves with vapor or oxidized compounds will lead to disturbances; such as oxide layer formations (particularly on the secondary side) with a corresponding retardant effect on the diffusion or a generally negative influence on the diffusion processes; and, moreover, the palladium-contained layers further tend at an elevated temperature present over lengthier time periods, to diffuse into the substrate so that the desired protective and disassociation effect will reduce with time. Pure palladium foils or foils homogenously containing palladium supported on a porous substrate must be constructed relatively thick, in order to be able to withstand the pressure differential encountered between the primary and the secondary side. This also fails to provide an inexpensive solution with respect to savings in the costs of the materials. Heavily constructed palladium-containing foils are, for the remainder, even more poorly suited for hydrogen diffusion than are thicker foils constituted of other materials.